Super Street Network

Project Porsche 944 Turbo: Part 4

Exhaust and brake upgrades

It's a candy store out there for Porsche 951s when it comes to performance upgrades. So many tuners to choose from, so many different parts, and I would test them all if I could. But, because of obvious limitations, I've got to be somewhat selective, and that's why the Porsche has so far received a Kokeln Stage V turbo, feeding the motor with copious amounts of air. At a moderate, 91-octane-friendly boost level, the car was already seeing 270 whp with the stock exhaust system in place. When Kokeln founder Dwain Dement finished tuning the car, I decided it would be best to drive it with a very mild boost level of 7.5 psi, good for a modest 170 whp and change--at least until I got a more free-flowing exhaust system installed in order to limit heat-soaking backpressure.

Next up was an aftermarket exhaust system, so I gave Performance Products a call (a major distributor of B&B Performance exhausts) and ordered its B&B header and cat-back exhaust system. B&B made no performance claims about the header system and said that the header was designed to be primarily just a factory replacement product. Apparently it's a common thing to crack headers on these 951s, especially the early '86 models, as the header systems did not come with a flex joint. B&B's header system features a slip-fit flange to avoid cracking, making it essentially a three-piece system and is made from 304 stainless steel.

When I looked inside the tubing, I was a little concerned to see what appeared to be two pipes that were welded together. I wasn't sure how it would affect flow, but as long as these headers flowed similar to stock, I thought they would be good enough to replace the factory units.

The car went to Precision Motion in Riverside, Calif., for the install. This family business has been around since the mid '70s servicing Porsches, including building several race motors that were run year after year at Daytona's 24-hour race. Now owned by long-time Porsche fanatic and mechanic Don Kravig, Precision Motion was my choice to get more work done on Project 951, starting with this exhaust system.

Luckily for me, Precision Motion has a loading Clayton dynamometer in the shop. Although, at the time, Don's computer software running the system didn't print out graphs like I'm used to seeing by the more widely used Dynojet dynos, I decided to test the headers anyway to see if at least the same power was sustained, given a certain constant load on the motor. How Don did this was by loading the car at wide-open throttle in fourth gear at selected rpm levels, and taking down the registered horsepower number the car was able to maintain before it couldn't accelerate any more and fell off--sort of like testing the car in an extreme, uphill situation. To get a proper test, we first had to get a new baseline with the factory headers still on, since Clayton dynos are notorious for spitting out ultra-conservative numbers when compared to a Dynojet.

At 7.5 psi, the car saw a maximum sustained whp level of 168 at 5500 rpm. Don then pulled the B&B headers and inspected them. Right off the bat he was impressed with the slip-flange feature. "The factory headers are such a pain to remove and re-install, but with this slip-flange design it should make it worlds easier to get this unit on and off, which could save a customer a few hundred bucks alone in labor costs," said Don.

When I showed him the piping inside, Don predicted that since the Porsche 944 Turbo's exhaust system was designed to all flow together, this B&B system may affect that and make us lose in the top end as long as we use the factory turbo-back system.

The factory headers indeed were difficult to get off due to the tight fit. Since the factory header studs stick so far out of the cylinder head, it came time to either shave the stud tips or lift the motor a half inch to slip the headers off. Precision opted to undo the motor from the motor mounts and lifted it just enough to slip one of the pieces from around one of the lengthy header studs. The B&B headers proved to be a really good fit with the cylinder head and the factory crossover pipe. With the shiny bends, they also looked pretty trick in the engine compartment.

Based on pricing alone, the B&B header system is a great alternative to buying new factory headers from the dealer to replace your cracked ones. Just for kicks, I called the local Porsche dealer here in Southern California and learned that not only are factory headers about $1,800 for both pieces, the labor alone will cost you an additional $736, bringing the grand total to $2,536, not including any possible extra labor to remove broken studs. The B&B headers featured here are $1,228 from Performance Products and took only 4.5 hours to install, bringing the grand total to $1,633, more than $900 in total savings over the dealer program.

When the dyno testing was all said and done, Don was right about the top end--the headers lost a few horsepower with the factory turbo-back exhaust system retained. But, much to our surprise, the gains in the low end were substantial. Between 3000 to 4000 rpm, the car was able to maintain between 17 to 18 more whp than with the factory headers, indicating a tremendous jump in low- and midrange torque of about 30 lb-ft, thanks to the boost kicking in a little sooner. What this header system essentially did was shift the power curve slightly to the left, which is nice for tightly turned racetracks and autocrosses, where torque is crucial, or even around-town driveability. However, it isn't be what you want for high-speed, straight-line performance.

Next up was B&B's cat-back system. Weighing in at 22 lb (5 lb lighter than the factory unit), the stainless-steel, two-piece design was a straightforward installation designed to fit with the factory 2.5-in. piping coming off the cats. When fired up, the car actually sported an exhaust sound, where before you could only hear the spinning timing belt from the front. The exhaust note, although relatively quiet, sung a nice, deep tune at idle. With a little throttle, the tune turned more into an exotic purr.

Back on Precision's dyno, the car was put to the test. With the new cat-back in, the low-end torque continued to increase, with a maximum gain of 7 lb-ft at 3000 rpm, while the top end opened up with 11 more hp at 6000 rpm. The midrange wasn't affected much at all. Peak horsepower was now matched to our 168 whp stock baseline at 5500 rpm, but the power curve flattened out nicely through 6000 rpm, now with 167 whp as opposed to 156 whp at that rpm with just the new header installed. Over stock, this was also a gain of 4 hp at 6000 rpm.

In the end, the B&B header and cat-back system together didn't affect peak power from the stock baseline, but a little more power was sustained through redline, and a large amount of torque was increased in the low end due to the system allowing the turbo to build boost sooner.

"If you're going to do the header system, you might as well get the cat-back system, too, since they worked pretty well together," Don said.

Performance Products also offers a 2.5-in. test pipe that eliminates the catalytic converter altogether. While I suspect the gain from removing the cat on a 944 Turbo would yield well in excess of 15 whp, this piece is legal for off-road use only. Unfortunately, other Project 951 time constraints prevented us from testing this pipe.

In anticipation of the power levels Project 951 eventually would be putting out, I had initially started the hunt for a big-brake upgrade. The stock system felt mushy and required a lot of force on the brake pedal to get the car to slow down. But, when I later realized the size of the factory Brembo four-piston calipers and rotors that came on all four corners, I decided to try out a good set of replacement rotors and pads first and see if that would take care of the problem. Since I was going to be working on the brakes, I figured changing the factory hard rubber lines to stainless steel and flushing the system with new, higher-temp brake fluid wouldn't hurt, either.

I ordered a set of front and rear Zimmermann cross-drilled factory replacement rotors, Pagid Orange pads, Goodridge stainless-steel lines and ATE Super Blue brake fluid. Right away, on their first application, the mushy brakes I had before were gone. The true feeling of four-piston brakes was back once again. The only downside is now I have to clean the wheels more often due to the Pagid race pads. But the extra performance is still well worth it.

Prior to these brakes, it was pretty hard to get the non-ABS braking system to lock up, but thanks to the new stopping power, it doesn't take nearly as much pedal effort to lock the tires up. Of course, I don't want to be locking up on the road, so it definitely looks like I'll have to soon go with wider wheels up front with stickier rubber to capitalize on the new braking performance. Stay tuned.

Maintenance As with virtually any 17-year-old car, I'm going to have to pay special attention to maintenance, especially with a high-performance car. I experienced this shortly after my purchase, when the lower radiator hose blew and leaked all the coolant onto the highway. Right then I decided I was going to replace all radiator hoses as soon as I could. Since it carries virtually everything I will ever need for maintenance, I grabbed my Performance Products catalog and started ordering--new lower and upper radiator hoses, a radiator-to-pipe hose, a new thermostat, thermostat housing and O-ring, both water pump-to-pipe hoses, an ex tank-to-pipe hose and an ex tank-to-water pump hose. To keep the motor running a little cooler, I also ordered a low-temp thermal fan switch.

As a motor gets used over a long period of time, it's possible for tiny metal particles to eventually make it into the oiling system from simple wear and tear. Performance Products carries a super strong oil filter magnet that traps virtually all small metal particles onto the walls of the oil filter, reducing the risk of them recirculating. It's easy to apply and is totally reusable.

The original oil pressure sending unit on Project 951 had been reading fine, but a noticeable leak around the edges made me replace it. Performance Products carries both single- and double-type factory senders, depending on whether or not it's to be used with an oil pressure light. --PM